As is known, the fuel injectors for direct injection engines that are commercially available at present comprise a main tubular body provided with a central through duct which terminates at one axial end of the tubular body in a spray nozzle adapted to atomise, in the combustion chamber, the high pressure fuel supplied within the duct, a shutter member mounted to move axially in the central duct to and from a closed position in which it obstructs the spray nozzle so as to prevent any discharge of fuel and a recall spring adapted to maintain this shutter member in the above-mentioned closed position.
Outside the main tubular body, the above-mentioned injectors further comprise a coil of electrically conducting material adapted to generate, when electric current passes through it, a magnetic field able to overcome the resilient force of the spring so that the shutter member can be temporarily moved from the closed position in order to enable fuel to be discharged. The shutter member is obviously made at least partially from ferromagnetic material.
As is known, fuel injectors for direct injection engines raise the problem of preventing the shutter member, in the closed state, after having violently struck the spray nozzle under the thrust of the spring, from rebounding repeatedly before settling permanently in the closed position. These rebounds have a major impact on the average life of the component and are the cause of undesired discharges of fuel following the theoretical moment of closure of the injector.
In order to remedy this problem, the shutter member at present comprises a bushing of ferromagnetic material mounted to move axially within the central duct, a closure pin mounted to move axially on the bushing with its point facing the calibrated hole that defines the spray nozzle and a resilient member interposed between the bushing and the pin so as to absorb the axial mechanical stresses to which the pin is subject when the point of the pin violently strikes the nozzle.
Unfortunately, the fuel injectors for direct injection engines described above have the major drawback that they are structurally complicated and therefore intrinsically not very reliable. Moreover, the injector assembly procedure is particularly time-consuming as a result of which the production costs of fuel injectors for direct injection engines are much greater than the production costs of conventional fuel injectors.